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Unit 9: The Database Model

Shared: All authorized users in an organization can share the information stored in its database. Notes
Integrated information is kept in the database for the purpose of sharing so that all user groups
may collaborate and accomplish the organization’s objectives.

9.1 Concept of Database Model

You are now opening to be grateful for the significance of the database move toward. You are
discerning the major benefits of mounting and using applications in a database environment.
Before proceeding further, allow us evaluation a few fundamental concepts and become
recognizable with some key expressions.
9.1.1 Data Repository

All data in the database reside in a data repository. This is the data storage space part where
physical data files are kept. The data depository contains the physical data. Mostly, it is a central
place of storage for the data contented.

9.1.2 Data Dictionary
The data repository contains the authentic data. Allow us say that you desire to keep data
about the customers of your business in your database. The arrangement of a customer’s data
could include fields such as customer name, customer address, city, state, zip code, phone
number, and so on. Data about a particular customer could be as follows in the respective fields:
Jane Smith/1234 Main Street/Piscataway/NJ/08820. There are two aspects of the data about
customers. One aspect is the structure of the data consisting of the field names, field sizes, data
types, and so on. This part is the structure of the data for customers. The other part is the actual
data for each customer consisting of the actual data values in the various fields.
The first part relating to the structure resides separately in storage, and this is called the data
dictionary or data catalog. A data dictionary contains the structures of the various data elements
in the database. It also contains the relationships among data elements. The other part relating
to the actual data about individual customers resides in the data repository. The data dictionary
and the data repository work together to provide information to users.
9.1.3 Database Software

Are Oracle and Informix databases? Oracle and Informix are really the software that manages
data. These are database software or database management systems. Database software supports
the storing, retrieving, and updating of data in a database. Database software is not the database
itself. The software helps you store, manage, and protect the data in a database.

9.1.4 Data Abstraction

Consider the example of customer data again. Data about each customer consist of several
fields such as customer name, street address, city, state, zip code, credit status, and so on. We
can look at customer data at three levels. The customer service representative can look at the
customer from his or her point of view as consisting of only the fields that are of interest to the
representative. This may be just customer name, phone number, and credit status. This is one
level. The next level is the structure of the complete set of fields in customer data. This level is
of interest to the database designer and application programmer. Another level is of interest to
the database administrator, who is responsible for designing the physical layout for storing the
data in files on disk storage.
Now go through the three levels. The customer service representative is just interested in what
he or she needs from customer data, not the entire set of fields or how the data is physically
stored on disk storage. The complexities of the other two levels may be hidden from the customer

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